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Friday, 9 March 2018

Intensified summer monsoon and the urbanization of Indus Civilization in northwest India

Yama Dixit, David A. Hodell, Alena Giesche, Sampat K. Tandon, Fernando Gázquez, Hari S. Saini, Luke C. Skinner, Syed A. I. Mujtaba, Vikas Pawar, Ravindra N. Singh & Cameron A. PetrieAbstractToday the desert margins of northwest India are dry and unable to support large populations, but were densely occupied by the populations of the Indus Civilization during the middle to late Holocene. The hydroclimatic conditions under which Indus urbanization took place, which was marked by a period of expanded settlement into the Thar Desert margins, remains poorly understood. We measured the isotopic values (δ18O and δD) of gypsum hydration water in paleolake Karsandi sediments in northern Rajasthan to infer past changes in lake hydrology, which is sensitive to changing amounts of precipitation and evaporation. Our record reveals that relatively wet conditions prevailed at the northern edge of Rajasthan from ~5.1 ± 0.2 ka BP, during the beginning of the agricultural-based Early Harappan phase of the Indus Civilization. Monsoon rainfall intensified further between 5.0 and 4.4 ka BP, during the period when Indus urban centres developed in the western Thar Desert margin and on the plains of Haryana to its north. Drier conditions set in sometime after 4.4 ka BP, and by ~3.9 ka BP an eastward shift of populations had occurred. Our findings provide evidence that climate change was associated with both the expansion and contraction of Indus urbanism along the desert margin in northwest India.

Location of (A) Urban Harappan sites at ∼4.6–4.5 ka BP and (B) Post- Urban Harappan after ~4.1–4.0 ka BP sites in NW India as denoted by the orange dots in each case. Note that the urban-Harappan sites are located on the margin of the Thar Desert and the post-urban Harappan sites are clustered to the right of paleolake Karsandi on the Indo-Gangetic plains. The location of Karsandi shown by the white triangle and other reported paleolakes in black triangles.

ConclusionsIt is increasingly evident that the landscapes across which Indus populations lived were diverse in terms of climate, geology and ecology, and the patterns of cultural behavior and response to climate variability are unlikely to have been uniform throughout the Indus region16,24. The paleoclimate record from paleolake Karsandi clearly suggests there were areas receiving favorable rainfall in the period leading up to the development of Indus urban centres along the northern fringe of the Thar Desert in NW India. This evidence underscores the importance of reconstructing local conditions for understanding the degree of adaptation and resilience of ancient civilization exhibited to climate change.